Antarctic ice-mass balance 2003 to 2012: regional reanalysis of  GRACE satellite gravimetry measurements with improved estimate of glacial-isostatic adjustment based on GPS uplift rates

Sasgen, Ingo; Konrad, Hannes; Ivins, E. R.; Broeke, M. R. van den; Bamber, Jonathan; Martinec, Z.; Klemann, Volker

doi:10.5194/tc-7-1499-2013

Cited by 80 publications

(100 citation statements)

References 54 publications

(101 reference statements)

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“…Previous studies have shown large negative mass imbalances and significant elevation losses for the nAP (Ivins et al, 2011;Shepherd et al, 2012;Luthcke et al, 2013;Sasgen et al, 2013;McMillan et al, 2014). However, in general these studies have not resolved the spatial distribution of mass imbalance in detail.…”

Section: Introductionmentioning

confidence: 88%

“…Glacier basins 1a,4a,6a,and 12a;c Glacier basins 19,[21][22][23][24][25]26b,[27][28][29][30]and 31a;d Glacier basins 17,18,and 19;e Our mass balance estimate for the nAP region agrees well with recently published gravimetric values. Recent GRACEbased estimates that can be most easily compared with our study yield values of −27.5 ± 10 Gt a −1 (summing the mascons encompassing and adjacent to our study area) (Luthcke et al, 2013), and 26 ± 3 Gt a −1 for a larger GRACE mascon extending to 70 • S (Sasgen et al, 2013). Due to the low spatial resolution of the gravimetric measurement, both these GRACE-derived results inherently include portions of the Larsen C ice shelf and adjacent ice-covered islands we did not measure (notably, King George Island) that lost elevation and mass during the ICESat period (Gardner et al, 2013).…”

Section: Discussionmentioning

confidence: 99%

“…A mapping of these patterns, over the entire region but at the glacier basin scale, can provide more insight into processes responsible for the ice loss. Studies based on gravitational change detection using the Gravity Recovery and Climate Experiment satellite system (GRACE) have an inherent spatial resolution of roughly 250 km scale (Ivins et al, 2011;Luthcke et al, 2013;Sasgen et al, 2013), far larger than the scale of the nAP individual glacier basins and islands. Past altimetry-based studies (Pritchard et al, 2009;Flament and Rémy, 2012;Shepherd et al, 2012;McMillan et al, 2014) suffer from either sparse coverage or slope correction issues, or both, due to the steep terrain in the nAP.…”

Section: Introductionmentioning

confidence: 99%

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Detailed ice loss pattern in the northern Antarctic Peninsula: widespread decline driven by ice front retreats

Scambos¹,

Berthier

Haran³

et al. 2014

The Cryosphere

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Abstract. The northern Antarctic Peninsula (nAP, < 66 • S) is one of the most rapidly changing glaciated regions on earth, yet the spatial patterns of its ice mass loss at the glacier basin scale have to date been poorly documented. We use satellite laser altimetry and satellite stereo-image topography spanning 2001-2010, but primarily 2003-2008, to map ice elevation change and infer mass changes for 33 glacier basins covering the mainland and most large islands in the nAP. Rates of ice volume and ice mass change are 27.7 ± 8.6 km 3 a −1 and 24.9±7.8 Gt a −1 , equal to −0.73 m a −1 w.e. for the study area. Mass loss is the highest for eastern glaciers affected by major ice shelf collapses in 1995 and 2002, where twelve glaciers account for 60 % of the total imbalance. However, losses at smaller rates occur throughout the nAP, at both high and low elevation, despite increased snow accumulation along the western coast and ridge crest. We interpret the widespread mass loss to be driven by decades of ice front retreats on both sides of the nAP, and extended throughout the ice sheet due to the propagation of kinematic waves triggered at the fronts into the interior.

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Section: Introductionmentioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Detailed ice loss pattern in the northern Antarctic Peninsula: widespread decline driven by ice front retreats

Scambos¹,

Berthier

Haran³

et al. 2014

The Cryosphere

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“…Reconciling these disparate estimates is an important problem. Previous studies have made use of satellite altimetry (Zwally et al, 2005), satellite gravimetry (Chen et al, 2006;Sasgen et al, 2013;Luthcke et al, 2013), or a combination of satellite and airborne data and climate model simulations (Rignot et al, 2011b) to provide estimates. In the latter case, the balance is found by deducting output ice flux from input snowfall in a technique sometimes referred to as the inputoutput method (IOM) or mass budget method.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous solution for mass trends on the West Antarctic Ice Sheet

et al. 2015

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Abstract. The Antarctic Ice Sheet is the largest potential source of future sea-level rise. Mass loss has been increasing over the last 2 decades for the West Antarctic Ice Sheet (WAIS) but with significant discrepancies between estimates, especially for the Antarctic Peninsula. Most of these estimates utilise geophysical models to explicitly correct the observations for (unobserved) processes. Systematic errors in these models introduce biases in the results which are difficult to quantify. In this study, we provide a statistically rigorous error-bounded trend estimate of ice mass loss over the WAIS from 2003 to 2009 which is almost entirely data driven. Using altimetry, gravimetry, and GPS data in a hierarchical Bayesian framework, we derive spatial fields for ice mass change, surface mass balance, and glacial isostatic adjustment (GIA) without relying explicitly on forward models. The approach we use separates mass and height change contributions from different processes, reproducing spatial features found in, for example, regional climate and GIA forward models, and provides an independent estimate which can be used to validate and test the models. In addition, spatial error estimates are derived for each field. The mass loss estimates we obtain are smaller than some recent results, with a time-averaged mean rate of −76 ± 15 Gt yr −1 for the WAIS and Antarctic Peninsula, including the major Antarctic islands. The GIA estimate compares well with results obtained from recent forward models (IJ05-R2) and inverse methods (AGE-1). The Bayesian framework is sufficiently flexible that it can, eventually, be used for the whole of Antarctica, be adapted for other ice sheets and utilise data from other sources such as ice cores, accumulation radar data, and other measurements that contain information about any of the processes that are solved for.

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“…Tamisiea et al 2007;Sasgen et al 2012), Antarctica (e.g. Sasgen et al 2007;Riva et al 2009;Sasgen et al 2013) and Fennoscandia, (e.g. Steffen et al 2008;Steffen & Wu 2011).…”

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confidence: 99%

The forward sensitivity and adjoint-state methods of glacial isostatic adjustment

Martinec

Sasgen

Velı́mský

2014

Geophysical Journal International

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S U M M A R YIn this study, a new method for computing the sensitivity of the glacial isostatic adjustment (GIA) forward solution with respect to the Earth's mantle viscosity, the so-called the forward sensitivity method (FSM), and a method for computing the gradient of data misfit with respect to viscosity parameters, the so-called adjoint-state method (ASM), are presented. These advanced formal methods complement each other in the inverse modelling of GIArelated observations. When solving this inverse problem, the first step is to calculate the forward sensitivities by the FSM and use them to fix the model parameters that do not affect the forward model solution, as well as identifying and removing redundant parts of the inferred viscosity structure. Once the viscosity model is optimized in view of the forward sensitivities, the minimization of the data misfit with respect to the viscosity parameters can be carried out by a gradient technique which makes use of the ASM. The aim is this paper is to derive the FSM and ASM in the forms that are closely associated with the forward solver of GIA developed by Martinec. Since this method is based on a continuous form of the forward model equations, which are then discretized by spectral and finite elements, we first derive the continuous forms of the FSM and ASM and then discretize them by the spectral and finite elements used in the discretization of the forward model equations. The advantage of this approach is that all three methods (forward, FSM and ASM) have the same matrix of equations and use the same methodology for the implementation of the time evolution of stresses. The only difference between the forward method and the FSM and ASM is that the different numerical differencing schemes for the time evolution of the Maxwell and generalized Maxwell viscous stresses are applied in the respective methods. However, it requires only a little extra computational time for carrying out the FSM and ASM numerically. An straightforward approach to compute the gradient of the data misfit is the brute-force method, whereby the partial derivatives of the misfit with respect to model parameters are approximated by the centred difference of two forward model runs. Although the brute-force method is useful for computing the gradient of the data misfit with respect to a small number of model parameters, it becomes expensive for a viscosity model with a large number of parameters. The ASM offers an efficient alternative for computing the gradient of the misfit since the computational time of the ASM is independent of the number of viscosity parameters. The ASM is thus highly efficient for calculating the gradient of the misfit for models with large numbers of parameters. However, the forward-model solution for each time step must be stored, hence the memory demands scale linearly with the number of time steps. This is the main drawback of the ASM.Key words: Numerical solutions; Inverse theory; Sea level change; Rheology: mantle. I N T RO D U C T I O NStudies on glacial isostati...

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Antarctic ice-mass balance 2003 to 2012: regional reanalysis of GRACE satellite gravimetry measurements with improved estimate of glacial-isostatic adjustment based on GPS uplift rates

Cited by 80 publications

References 54 publications

Detailed ice loss pattern in the northern Antarctic Peninsula: widespread decline driven by ice front retreats

Detailed ice loss pattern in the northern Antarctic Peninsula: widespread decline driven by ice front retreats

Simultaneous solution for mass trends on the West Antarctic Ice Sheet

The forward sensitivity and adjoint-state methods of glacial isostatic adjustment

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